INVESTIGATION OF MERCURY DEPOSITS, CINNABAR CREEK

AREA, GEORGETOWN AND AKIAK DISTRICTS,

KUSKOKWIM REGION, SOUTHWESTERN ALASKA

BY F. A. RUTLEDGE

* * * * * * * * * Report of Investigations 4719

UNITED STATES DEPARTMENT OF THE INTERIOROscar L. Chapman, Secretary

BUREAU OF MINESJames Boyd, Director

Work on manuscript completed May 1950. The Bureau of Mines will welcome reprintingof this paper, provided the following footnote acknowledgment is made: oReprlnted fromBureau of Mines Report of Investigations 4719."

November 1950

INVESTIGATION OF MERCURY DEPOSITS, CINNABAR

CREEK AREA, GEORGETOWN AND AKIAK DISTRICTS,KUSKOKWIM REGION, SOUTHWESTERN ALASKA

by

F. A. Rutledge-,

CONTENTS

PageIntroduction and summary . .................. ........... 1Acknowledgments............................ . 1Location and accessibility . . ...................... 2....... 2Physical features and climate.................. . ........... 3History and production ............................. . 3Property and ownership ................................ 4General geology. . . 5Description of the deposits ............................. . 6

Lucky Day lode .............................. 6Redskin lode .. ............................ . 8Broken Shovel lode claim ...................... . ....... 8Cinnabar Creek placer area .................... 9

ILLUSTRATIONS

FollowsFig. 22Ze1. Index map of Alaska .................... 22. Holitna River area..................... . . 23. Mercury deposits, Cinnabar Creek area .............. 44. Canary Gulch mercury deposits .. .. 65. Luc-ky Day lode.................................... 66. Cinnabar Gulch and Broken Shovel Gulch area .... 87. Cinnabar Creek placer area .... 8

i/Mining engineer, Juneau, Alaska.

Report of Investigations 4719

INTRODUCTION AND SUJMMARY

Mercury deposits were discovered in 1941 in the sedimentary rocks of theCinnabar Creek area, near the head of the Holitna River drainage in south-western Alaska, by Russell Schaefer and Harvey Winchell of Sleitmut, Alaska.High-grade float was found in both Canary Gulch and Cinnabar Gulch, andindications of other deposits were found in Alder and Broken & ovel Gulches,Schaefer and Winchell's exploration in 1942 and 1943 revealed placer depositsof cinnabar along Canary Gulch. During prospecting on Canary Gulch, 3,600pounds of ore was recovered from the detrital material on the Lucky Day lodeat the head of the gulch. When retorted, this ore was reported by the ownersto have produced 26 flasks of quicksilver.

During the summer of 1945, Wallace M. Cady and Charles A. Hickcox, ofthe U. S. Geological Survey, spent 4 weeks mapping and investigating theareawg/ Bruce I. Thomas and Harold C. Pierce, mining engineers of the Bureauof Mines, examined and sampled several deposits in September 1943. Followingtheir preliminary examination, in view of the exceptionally high-gradecinnabar present, additional investigation by the Bureau of Mines was re-commended. A program of trenching, test pitting, and sampling to delimitthe deposits was completed during the summer of 1947 under the direction ofthe author.

ACKNOWLEDGMEJTS

The field investigations of the former Mining Division of the Bureau ofMines in Alaska daring-this period were under the general direction ofR. S. Sanford, acting chief, Alaska Branch.

Chemical analyses included in this report were made at the Salt LakeCJtyExperiment Station of the Bureau of Mines under the general supervision ofS. R. Zimmorley, Chief, Salt Lake City Branch, former MIetallurgical Division.Analyses wore made by H. E. Peterson, metallurgist.

Acknowlegment is made also to Bruce I. Thomas and Harold C. Pierce,mining engineers of the Bureau of Mines, for the preliminary examinationof the deposits. Special reference is made to the report by Wallace M. Cadyand Charles A. Hickcox of the U. S. Geological Survey.

J Cady, Wallace M., Quicksilver Deposits in the Cinnabar Creek Area,Georgetown and Akiak Districts, Southwestern Alaska: U. S. Geol.Survey Preliminary Report, 1944, 7 pp.

3838 -

Work on the project was greatly facilitated by the help of RussellSchaefer, Sleitmut, Alaska. The author is indebted to Mr. Schaefer fororiginal sampling and sketches, past-production figures, and invaluableassistance during the project.

The data on the results of sampling the mercury placer ground alongCinnabar Gulch by the New York-Alaska Gold Dredging Corp., received throughthe courtesy of James K. Crowdy, Vice President and Managing Director, isalso gratefully acknowledged.

LOCATION AND ACCESSIBILITY

The mercury deposits of the Cinnabar Creek area lie in the southernpart of the Georgetown and Akiak districts on the divide between the drainageof the Aniak and HolitnaRivers. Both the Aniak and Holitna Rivers headin the Kilbuck Mountains of Southwestern Alaska and flow north to theKuskokwim River.

Figure 1 is an index map of Alaska showing the location of the HolitnaRiver area. The mineralized area is on the upper Holitna River, 85 milesby air southwest of Sleitmut, or approximately 200 miles by the water routeup the Holitna River and its tributaries (fig. 2). The deposits are nearlongitude 1580 50' W., latitude 600 45t N.

At ordinary stages of water during the summer, the Holitna River and itsupper tributaries are navigable by small power boats to within 20 miles ofthe deposits. At moderately high stages of water, the tributaries can benavigated to within 1 mile of the deposits by using a poling boat and out-board motor. The upstream trip from Sleitmut to the area requires a weekto 10 days, and the return trip about 4 days. The tributaries of the HolitnaRiver are blocked by numerous beaver dams, which makes progress difficult andslow.

There are no airplane landing strips in the area. A small lake at the.head of Gemuk River, within 15 miles of the deposits, is lprge enough forsmall float ships, During the examination, ski planes were landed on thedivide between Beaver Creek and Gemak River, about 2 miles northeast fromCanary Gulch. If desired, a landing strip could be constructed at thislocation without excessive cost.

Another means of access into the area is by tractor trails. One trailleads from the head of Cinnabar Creek across the divide' and down WaterboatCreek to the Aniak River, where it connects with the tractor trail up theAniak. This route was used by the New York-Alaska Gold Dredging Corp. whenthey sampled the placer along Cinnabar Creek in 1943.

For the program of development by the Bureau of Mines, a D-4 tractor wastaken from Noga1ut, on the Holitna River, to the project area during thespring of 1947. (See fig. 2.) The trip was made on the snow before breakup,

3838 -2-

°-74 /7S' /62'50'

HOIN RIVER /AREAC CR O

Figure 1. - Index map of Alaska.

MODIFIED FROM AAF PRELIMINARY BASE

SCALE OF MILES MAP 1180

NOVEMBER 15, 947 CAT TRAIL

Figure 2. - HoT itna River area.

and undoubtedly part of the route along the Holitna River would have beenimpassable during the summer months. At the close of the project, the equip-ment was taken to the camp of the Poandori Placer Mining Co. on Cripple Creek,The previously mentioned route made by the New York-Alaska Gold DredgingCorp. was followed to the Aniak River. Unable to cross the Aniak River atthis point because of high water, it was necessary to break a new trail upthe Aniak nearly to the head of the river before a crossing could be made.The route followed is shown in figure 2. If conditions had been known, itwould have been possible to pick a shorter and better route across the divideat the head of Beaver Creek into the Aniak Valley.

PHYSICAL FEATURES AND CLIMATE

The area is characterized by low, moderately rolling hills, but sharp,rocky peaks are conspicuous at a few of the crests. The hills are coveredwith a mantle of moss, which overlies residual rock material of variousthicknesses. The gulches and upper creek valleys that drain the area aroabove timberline but support a thick growth of alders and scrub willows. Thelower valleys support a good stand of spruce.

At tho north end of the area is a large butte capped by olivine basalt.Several other similarly capped hills are found in the Aniak Valley west ofthis area.

Spruce suitable for lumber and mine timbers can be obtained along thedivide between Beaver Creek and Gemnk River, 1 to 2 miles east of the LuckyDay lode, and also along the valleys several miles below Canary Gulch. Themajority of the trees are 1 to 1-1/2 feet in diameter, and the average heightis about 35 feet. The trees, being close to timber line, are heavily branchedand taper rapidly and are therefore poor for lumber.

Climatic records from the area are not available. The nearest record-ing station is at Aniak in the valley of the Kuskokwim River. Here theannual precipitation for the 6 year period ended in 1946 was 19.74 inches,including the moisture from 8 to 10 feet of snow. The mean annual tempera-turo was 27.430 F. As the Cinnabar Creek area is about 1,300 feet higherthan Aniak, it is probable that lower temperatures occur at the higherelevation. The "freeze-up" begins in September, and the "break-up" usuallyoccurs around the middle of May.

HISTORY AND PRODUCTION

No organized party had done geological reconnaissance work in the areaprior to the summer of 1943, and the upper Holitna River region was virtuallyunexplored as far as its mineral resources were concerned.

Russell Schaefer and Harvey Winchell of Sleitmut located and sampledthe Lucky Day lode in Canary Gulch in the summer of 1941 and also locatedplacer claims on Cinnabar Gulch, Cinnabar Run, and Cinnabar Creok. Floatalso was discovered in Alder Gulch and Broken Shovel Gulch.

3838 -35

In September 1941 Herschel Landru located the Broken Shovel lode claimon upper Broken Shovel Gulch. He also located placer claims on CinnabarCreek below those of Schaefer and Winchell. During October of the same year,Kenneth Deleray, engineer for the Bristol Bay Mining Co., sampled the placerdeposits of Cinnabar Gulch and the Lucky Day lode deposits. The local namesCinnabar Creek, Cinnabar Run, and Cinnabar Gulch designate, in order, themain creek, the main northern tributary, and its eastern tributary, as shownin figure 3.

During 1942, Schaefer recovered 2,300 pounds of cinmabar ore fromdetrital material from the Lucky Day lode and from it retorted 15 flasksof mercury. In the spring of 1943, the New York-Alaska Gold Dredging Corp.prospected and sampled the placer deposits on Cinnabar Gulch and CinnabarCreek. In the summer of the same year, Schaefer recovered an additional1,300 pounds of cinnabar ore from the residual material of the Lucky Daylode, which yielded 11 flasks of mercury. No ore was taken from the lodeitself.

PROPERTY AID OWNERSHIP

Tho mining rights of all the claims staked in this area were held bythree individuals, two of whom were partners. The following tabulation showsthe original ownership of these claims and their locations:

Claims staked by Russel R. Schie-for and Harvey Winchell, partners,Sleitmut, Alaska.

Name LocationLode Claims

Lucky Day Discovery Canary GulchLuck Day No. 1 Canary GulchRedskin Alder Gulch

Placer Claims

Discovery Cinnabar GulchNo. 1 Below Discovery Cinnabar RunNo. 2 Below Discovery Cinnabar RunNo. 3 Below Discovery Cinnabar CreekNo. 4 Below Discovery Cinnabar CreekNo. 5 Below Discovery Cinnabar Creek

Claims staked by Herschel Landru, Fairbanks, Alaska

Name LocationLoade Claims

Broken Shovel Broken Shovel GulchPlacer Claims

No. 6 Below Discovery Cinnabar CreekNo. 7 Below Discovery Cinnabar Creek

3838 4

* a* SCL OF MILS

-~~~~~~~~11 LEGECKY,r * LIMITS OF TIKCHIK ICE SHEET

*..: ALUIM;OIIN AATFOGelg byW .Cd .A ikx . S. GelgclSre

F i .u .e 3.. . - Me rcu ry depo C i C ee* I~~~~~~~~~~~~GL4

* 5 *~~~~~~~~~~~~~'I '

* S. * ~ ~ ~ ~ ~ ~ OD

* *~t; * : .* *:

*5**2*3,

* . . .5.. *. /~# 17

INEREDE GRYACK AN SHAL

ALLUVIUM * OLIVINE BASALT FLOW

Geology by W. M. Cady & C. A. Hickox, U. S. Geological Survey

Figure 3. - Mercury deposits, Cinnabar Creek area.

All of the aforementioned claims were recorded at the office of theU. S. Commissioner at Aniak, Alaska.

GENERAL GEOLOGY

The following discussion of the geology of the area is quoted fromthe report by Cadyg .

The bedrocks of the Cinnabar Creek area include a suc-cession of interbedded graywackes, shales, argillites, and'lavas.Most of these rocks are of Triassic age, but sediments of pro-bably Cretaceous age crop out in the southwestern part of thearea. Some zones in the Triassic rocks contain considerablechert, with minor limestone. The sedimentary rocks are intrudedby sills probably of Tertiary age. Most of the sills and flowsare of basalt, commonly porphyritic. A flow of rather coarse-grained, porphyritic, olivine basalt lies across the upturned anderoded edges of the bedded rocks in the northern part of the area.

Some of the sills are hydrothermally altered to a lightpearl-gray rock, which weathers yellow-brown and resembles thetypical "yellow-rock porphyry" in the Sleitmut area. Some ofthe graywacke also appears to be altered. The altered rocksform a northward-trending belt about a mile wide and at least6 miles long. Altered sill rock appears 'to be present morecommonly &t higher elevations immediately beneath remnants ofthe rolling upland surface than at lower elevations in thegulches, although this may be only because of better exposuresnear the hilltops.

The general strike in the belt of altered sill rocks isbetween N. 25° W. and'N., although the regional strike of thesediments is northeasterly. In the belt of altered rocks thedip in general is steeply west.

Frost-broken rock fragments mantle the hills to a depthof as much as 5 feet, but the fragments are not far enough re-moved from their bwdrock sources to interfere seriously withthe tracing of geologic contacts Of "yellow rock" or floatore. In the valley lowlands are deep alluvial deposits, which,according to prospectors, contain cinnabar concentrations nearthose places where they traverse the telt of altered sills.

The topography of the hills in the 'vicinity of the quick-silver deposits was developed during 'at least two cycles oferosion; first, formation of a late matu're surface and second,incisions to form youthful steep-walled gulches, leaving only,remnants of the earlier surface in the't-olling upland areas.

. See footnote 2.

* DESCRIPTION OF THE DEPOSITS

Lucky Day. Lode

The Lucky Day lode deposits lie along and. near the head of CanaryGulck, a small tributary on the left limit of Beavrer Creek (fige. 3 and 4).

Mineralization is of two types. Along Canary Gulch, the quicksilver occurs

as thin, sparse films of cinnabar associated. with quartz and stibnito along

bedding-plane faults, cross joints, and zones of brecciation in the gray-wacke and shale. A small amount of motallic mercury also is present..

Mineralization of this type has boon traced over an area 350 foot long

and 50 feet wide along the right limit of Canary Gulch. One cut 175 feet

long, paralleling the gulch, was partly completed before mechanicalfailure of the tractor dozer precluded further developmont-by dozer trench-

ing. The mineralized zone was exposed by several open cuts and in one of

the caved adits that was reopened, Three samples of th6 highest-grade

showings of this area were taken by the Bureau of Mines. The location of

these samples is shown in figure 4, and the results of analysis in table 1:

TABLE 1. - Analysis of samples, upper Canary Gulch

Width, Mercury, Antimony,Sasmle f' eet percont Percent_ ; _ ~~~~~, .p!r- -

9....,.. 1.1 0. 31 0.16l0...... 1.1 .18 .19

, E 1~.7 .07 11.15

The results of additional sampling of this deposit by the owners in

1942 are given through the courtesy of Russell R. Schaefer. Each sample was

taken over a sample length of 5 feet normal to the strike of the mineralized

area. Location of the exposures sampled is designated by the letters A, B,

C, E, and F in figure 4, and the results of analysis are given in table 2.

TABLE 2. - Analysis of Schaefer's and WinchollIs samples,upper Canary Gulch. (Seo figs. 3 and 4)

Type of Mercury,Sampl j opening percent

A-1...*Q Adit TraceA-2 .. i do. o.o8A-3.... do. .03A-4 .,.00 do. .07A-5.....I do. .10A- 6..... do. .03A- 7...... do. .03

3838 -6-

SAPL I=-

0 100 200 300 400

/ SCALE OF FEETMAY 1947

Figure 4. - Canary Gulch mercury deposits.

I~~~~~~~~~~~~~/ ,-

0 l0 20 30 40 30 SHAFT A

SCALE OF FECT

MAY 13, 1047~ ~ ~ ~ ~~~~~~~~~~~~~~RA AC~SAML I

SAMPLE E 42

G1 // 9 CRAY WACKE

S/MP 1/ 3LEGEND

SAMPLE 6 eS X - ~~~CINNA8AR MINERALIZATIONSAMPLESAMLE6

L BASALT INTRUSIVE

/ /| H GRAYWACKE

SAMPLE RESULTS

SAMPLE WIDTH MERCURY ANTIMONYNO FEET PERCENT PERCENT

I II1 157 1.4

2 2.9 1.6 0.353 0.8 7.9 0.654 0.6 14.8 3.05 2.2 3.2 0.556 2.8 0 327 1.7 0.06 0448 0.8 8.6 . 1.2

Figure 5. - Lucky Day lode.

TABLE 2. - Analy sis of Schaefeors and Win2c e ol I sgle

Typeof ;Mercury,Saple topening pgrcent

B-1 'Adiit 13B-2 .... do..B-e... i do. .04B- 4 . j do. .05

- 0~~~~~~~~~~~B-15..... do. .04

C-1 | ~do 002C-2..... do. .01C-3.....l do. TraceC-4. j i do, MacoC-5 ...0.i do. 0.02

Cdo. ; .05C-70. do. .04

E-l.....t ? do. .10E-2. .... do. .03

F-1..... Pit .55F-2. l do. 12

This zone of cinnabar has boon sampled over a length of 310 feet and

has an average width of 11 feet.

The second type of mineral deposit is directly associated with the sill-

like intrusives of basalt in the graywacke near the head of Canary Gulch.

(See figs. 4 end 5. ) These occurrences consist off lenticular pods of nearlymassive cinnabar paralleling the intrusivos and narrow offshoots of lower-grade cinnabar mineralization along bedding-plane faults between the high-grade pods and the intrusives. All of the production of quicksilver fromthis area has been obtained by retorting hand-sorted ore derived from thesesmall high-grade occurrences.

High-grade ore was revealed in two of the orgint1 test pits in the area

by Schaefer and Winchell. Part of the hand-sorted ore recovered by them was

from-theso pits, but the main production came from open cuts along a zone

of placer concentration below the deposits at the head of Canary Gulch.

A bulldozer trench was excavated along the strike of the ore zone during

1947 by the Bureau of Ivnes (sOO fig. 5). Of the six samples taken in themineralized zone, three samples were representative of the high-grade lenti-

cular pods of cinnabar, and the reamining three were taken across the mineral-

ized bedding-plane faults between the lenses and the intrusive, The mineral-

ized material consisted primarily of cinnabar, stibnite, and quartz associated

3838 -7-

with altered graywacke and basalt* A small amount of metallic mercury ispresent.

Only the northeast end of the ore zone was actually delimited. Thesouthwest end was inferred from the barren test pit 30 feet southwest of thelast exposure and the lack of float in the bulldozed trench. In all caseswhere a mineralized zone of cinnabar was exposed in the area, a concentrationof float was found on the bedrock extending downhill from the outcrop.

Two shallow shafts were sunk on the ore zone to ascertain the downwardextension of the lenses. One lens measured 6 feet along the dip and theother 4.5 feet. In each case the mineral deposit pinched out along thebedding planes, as shown in the cross sections of shafts, (fig. 5).

Two samples were taken of a brecciated zone of graywacke near the southend of the trench. These samples (numbers 6 and 7) contained metallicmercury, a small amount of cinnabar, and some stibnite.

Another occurrence of interest, though not of economic consideration,is a light-gray basalt sill on the ridge a short distance northwest of themain deposit.

Redskin Lode

The Redskin lode claim (fig. 3) at the head of Alder Gulch was examinedbriefly during this investigation, but the hiineral deposit did not warrantadditional investigation. The deposit is approximately 1-1/2 miles southof the Lucky Day lode.

Mineralization at the Redskin lode is almost identical to that alongCanary Gulch. The cinnabar occurs as sparse films along bedding planes,cross joints, and zones of brecciation in the graywacke and shale.

Broken Shovel Lode Claim

The Broken Shove-l.deposit (fig. 3) outcrops on the ridge east of BrokenShovel Gulch (fig. 6) and to the east of the claim staked by Herschel Landrualong the gulch. This deposit lies in the watershed of the Aniak River471/2 miles north of the Lucky Day lode.

Several shallow prospect pits were excavated by Landru in an attemptto trace the float back to its source. The main showing (marked outcrop onfigure 6) is a narrow, irregular vein of quartz locally containing smalllenses of stibnite and minor amounts of cinnabar. Several smaller and lesspersistent quartz veins are present and may have furnished a part of theplacer cinnabar in Broken Shovel Gulch.

3838 -8

0 ~ ~ ~ ~ /

0 0~~~~~~~~

0f - soo lC *\ 00~~

DI=SC LACERET

[ * ~~Mdiid from U. S. Geologia Surey ma

Figure 6. - Cinnabar Gulch and Broken Shovel Gulch area.

(/4f4

4CINNABAR GULCH

X - DISCOVERY L

1~~.,~ 4/q 34~~~~ I / -J~~~~CAII, 600 /e

e0 '\%o .e} i

\\ s\

NO.~~~~bU-tit~\q ' NT

TEST P IT DEPTH MERCURY \O 4," KTHNTT CLN MI N ING POUNDS SKETC NO TO CALNO. SECTION PER CU. YD. -,

40 10.5 0.84 C-P45 14.0 0.34 \s *%

25 13.0 0.54 4.0,53 10.0 0.0025 8.0 0.42 445 7.0 0.0065 5.0 0.00I 6 5.0 0.27

4 0 6.0 0.367 0 5.0 0.40 COMPILED FROM INFROMATION14 9.0 0.32 SUBMITTED BY J.K. CROWDY

42 5.0 0.40 MANAGING DIRECTOR50 8.0 0.00 NEW YORK-ALASKA GOLD DREDGING CORP.88 5.5 O.?21 NYAC, ALASKA

Figure 7. - Cinnabar Creek placer area.

Cinnabar Creek Placer Area

High-grade placer cinnabar was found along Cinnabar Gulch, CinnabarRun, and the upper portion of Cinnabar Creek below Cinnabar Run, and testpits by Schaefer and Winchell traced the cinnabar to the cluster of testpits shown in figure 6 upstream from the Discovery claim. As the pitsupstream contained only a minute amount of cinnabar, and the cinnabar recov-ered from the pits in the area was extremely angular and showed very littlesigns of wear, it was supposed that the original source of the cinnabar waswithin this area.

A 390-foot bulldozer trench was started by the Bureau of Mines to ex-pose the bedrock across this area and if possible locate the original sourceof the placer cinnabar. To accelerate excavation of the trench, a small damwas built across Cinnabar Gulch and material loosened by the bulldozer wasground sluiced from the trench. Maximum depth to bedrock was 18 feet.

No lode occurrence of cinnabar was found. Placer cinnabar was dis-tributed on bedrock throughout the length of the trench, though the degreeof concentration varied. In appearance, the grains and nuggets are similarto those found later nearer the head of the gulch. The source of thecinnabar may be the altered basalt sill crossing the head of Cinnabar Gulchand the narrow quartz stringers associated with it, like that outcroppingat the Broken Shovel lode.

Cadyl/ describes the placer deposits in the Cinnabar Creek area asfollows:

The known placer deposits in the area are in CinnabarGulch and in the valleys of Cinnabar Run and Cinnabar Creek. Theyconsist of high-grade ore nuggets in alluvial material. The paystreak, which heads in Cinnaber Gulch, is regarded as probablytypical of others in creek valleys not yet tested. Near thehead of this pay streak the nuggets, averaging about the sizeof a walnut, are angular, but a claim length downstream, whereCinnabar Gulch enters the valley of Cinnabar Run, they are ratherwell-rounded. Thus, it is inferred that the bedrock source of thecinnabar was not far from the head of the pay streak. Remnants ofa bench 40 feet above the bottom of Cinnabar Run, south of theconfluence of Cinnabar Gulch and Cinnabar Run, appear to have heldparts of a pay streak from which several large, well-roundedcinnabar nuggets have slumped to the rim of the present flood plain.

During 1941-42 Schaefer and Winchell sank several test pits in thevalleys of Cinnabar Creek, Cinnabar Run, and Cinnabar Gulch to trace the paystreak of placer cinnabar. The results influenced the New York-Alaska GoldDredging Corp. (Nyac) to prospect and test the ground during 1943, as shownin figure 7.

The valleys of Cinnabar Run and Cinnabar Gulch are narrow, 100 to 150feet wide, with steep slopes. Alluvium averages about 10 feet thick and iscomposed of slide rock and washed gravels.

N See footnote 2.

3858 -9-Interior - Bureau of Mines, Pittsburgh, Pa.